Use flake8-import-order plugin

In reviews we usually check import grouping but it is boring.
By using flake8-import-order plugin, we can avoid this.
This flake8 plugin is already used in tempest.
It enforces loose checking so it sounds good to use.

Note that flake8-import-order version is pinned to avoid unexpected
breakage of pep8 job.

Change-Id: I8ccd05eb70350a2441cc2a4d1eafc09ee690b83b

openstack_dashboard/api/heat.py

@@ -11,16 +11,16 @@
 # under the License.
 
 import contextlib
-import six
-from six.moves.urllib import request
 
 from django.conf import settings
-from oslo_serialization import jsonutils
-
 from heatclient import client as heat_client
 from heatclient.common import template_format
 from heatclient.common import template_utils
 from heatclient.common import utils as heat_utils
+from oslo_serialization import jsonutils
+import six
+from six.moves.urllib import request
+
 from horizon import exceptions
 from horizon.utils import functions as utils
 from horizon.utils.memoized import memoized

openstack_dashboard/test/api_tests/heat_rest_tests.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import json
+
 import mock
 
 from openstack_dashboard import api

openstack_dashboard/test/helpers.py

@@ -19,6 +19,7 @@
 import collections
 import copy
 from functools import wraps
+from importlib import import_module
 import os
 import traceback
 import unittest
@@ -35,7 +36,6 @@ from django.utils import http
 from cinderclient import client as cinder_client
 import glanceclient
 from heatclient import client as heat_client
-from importlib import import_module
 from keystoneclient.v2_0 import client as keystone_client
 import mock
 from mox3 import mox

tox.ini

@@ -123,6 +123,7 @@ ignore =
 # H904 Delay string interpolations at logging calls
 enable-extensions=H203,H904
 max-complexity = 20
+import-order-style = pep8
 
 [hacking]
 local-check-factory = horizon.hacking.checks.factory